Electromechanical transformer

ABSTRACT

This disclosure describes an ancient mechanical device which has been improved by modern machine tools, lubricants, ball bearings, and now by electromagnetics. A gear reducer/increaser with the use of magnetic bearing technology changes a friction dominated device into an element that can operate efficiently indefinitely in any environment with a range of operation heretofore impossible. Backlash, an inherent weakness of prior precision geared systems is small and controllable. This device can convert linear or rotational motions at specific force or torque levels to larger or smaller displacements with reciprocal changes in force or torque to preserve conservation of energy. It can be constructed in a variety of forms, with circular and concentric form gaining advantages of symmetry mechanically, less stray magnetic flux, and better “copper” utilization electrically. A design of general utility showing a device of this type is illustrated and described not to limit variations for needs, materials, or methods of manufacture but to illustrate the parts and their function.

BACKGROUND

The inclined plane is one of the simplest fundamental mechanical devices, its use was employed in the construction of the pyramids. The advent of machine tools saw the introduction of screw threads and screw jacks with which a single man can lift a building. High precision worm gears exhibit tremendous mechanical advantage in a single pass. All of these had obvious limitations due to friction. The performance and speed of operation took a big step forward in recent years with the introduction of ball screws with recycling balls which greatly reduced sliding contact.

In the 1960's magnetic bearings were invented and developed*, providing not only near frictionless support but eliminating the need for lubrication which allows such systems to be employed in clean rooms, medical facilities, and food processing plants. The lack of physical contact can eliminate wear and allow lifetimes independent of speed.

For inclined planes and screw-type actuators, the orders of magnitude lower friction opens a whole new range of applications and dramatically improves efficiency. Friction in screw jacks is so large that it is depended on to prevent large loads from back driving. Active electromagnetic forces can be switched on or off at will.

I have called this device an electromechanical transformer since it is a bidirectional device, allowing input torques (or forces) to produce multiplied output forces (or torques) with corresponding displacement reduction; the product remaining constant just as the volt current ratio of an electrical transformer behaves. and at equally high efficiency.

*Magnetic Bearings for Spacecraft NASA/GSFC X 721-72-56 P. A. Studer January 1972

SUMMARY

The Background has given some historical perspective on the evolutionary development of former devices of this type and stated that a development in electromagnetics has changed a fundamental limitation on their design and performance. How magnetic bearing technology can be implemented to effect this result is the subject of this disclosure.

Magnetic bearings have been designed to control many axes, most commonly radial and axial. It has been found that they are most effective when permanent magnet (bias) flux is introduced into the region to be controlled, as in these illustrations.

If permanent magnets cause each of the two parts to be of opposite polarity, magnetic flux will flow between the two, largely where they are closest. If a gear tooth, for instance, of a magnetically polarized worm gear passes between two teeth of another gear, flux will be passing to the right and to the left, equally if it is centered. If a sensor providing a signal proportional to a gap be fed to an amplifier supplying current to conductors below the central tooth, it can increase the flux on one side and lessen the other. Forces proportional to the sq. of the flux density can be produced to keep the tooth centered against external forces. These forces are also proportional to the area over which the flux acts and the net force of these oppositely directed forces acts to move or hold the tooth centered and free of contact even when carrying rated loads.

Mechanically, the behavior of these devices is exactly as expected, determined by well known rules of mechanics, over a greater range of operation than was formerly possible due to frictional limitations.

In addition to the filing date (08/28/20060 granted to this application Ser. No. 11/510,818=1 claim the benefit of Aug. 29, 2005 granted to Provisional Application 60/711,874

SPECIFICATION

The basis for this device is the inclined plane in which a heavy object can be moved vertically by a relatively smaller force exerted laterally over a greater distance, as was known since ancient times.

A more compact version of this device is the common screw thread in which the inclined plane is made circular, forming a helix such as is in bolts, nuts, or worm gears. Thus a rotary to linear motion device is created.

The limitations of these devices are the result of friction which has been alleviated by lubricants and more recently by ball bearings. Reduction of friction also allows bidirectional operation of these devices, allowing linear to rotary and rotary to linear motions.

This disclosure describes and illustrates a new means for further improving their operation such that still less energy is dissipated and long lifetimes, even in fast repetitive actions is obtained, by incorporating new electromagnetic control methods, known as magnetic bearing technology. By these means, the working surfaces are kept separated by magnetic forces and non-contacting operation allows virtually friction-free movement with no wear debris and with immunity to the operating environment.

FIGS. 1A and 1B show an elemental magnetic bearing structure, the central element consists of high permeability circular plates between two facing permanent magnets which generate large magnetic flux toward both the upper and lower stator surfaces. Currents flowing in the surrounding circumferential coil produce magnetic flux across the same two gaps either upward or downward depending on the direction of current flow. These fluxes add to the steady state flux in one gap and subtract from the flux in the other. Since the force produced by the total magnetic flux between these surfaces is proportional to the square of the flux density, large differential forces are produced. The central element, when the coil current is controlled with respect to its displacement from the centered position, may be suspended and free to rotate with no physical contact. The application of these principles to the inclined plane is the essence of this invention.

FIG. 2 shows diagrammatically the application to the more generally useful compact form in which the surfaces are made in a helical manner for continuous increase of the length of these mating surfaces and the space available for the control coil.

This device, as shown in FIG. 2, consists of two elements of opposite magnetic polarity, engaged as a screw and nut, with one thread typically in a slot or recess of the other, such that magnetic flux flows through each gap in opposite directions leading to balanced forces when the surfaces are equidistant and the flux density the same in both directions. This position is inherently unstable, therefore a control magnetic flux is made to pass unidirectionally through both gaps where it will generate differential forces by increasing the flux in one gap and decreasing it in the other. Reversing the direction of the current providing this control flux reverses the direction of the differential force in proportion to magnitude of the control current. By the use of a position sensor or other suitable information and well known servo techniques, it achieves the application of magnetic bearing technology to a variety of common mechanical inclined plane structures. These include simple wedges, worm gears, and a whole class of mechanical devices based on the inclined plane, commonly found in screw threads.

FIGS. 3 A&B, show a section of the assembled construction of two engaged helices, of permeable material, between which magnetic flux from a constant bias source (1) passes. This flux divides into both axial directions to mating teeth on (5) after which it rejoins and returns to its source via continuous gap (7). Control flux, shown separately for clarity, all teeth carrying nominally the same total flux, increases the flux density in one direction and decreases it in the other gap. This differential flux density produces the desired axial force, as a function of the magnitude and direction of the control current, itself a function of the axial error signal. This control is exercised to maintain gaps (8) and (9) equal, eliminating all axial contact and, with radial control maintaining concentricity, assures both zero contact and no backlash within the limits of the controller.

The concentricity can be maintained by conventional bearings or magnetically, preserving a totally noncontacting device, as illustrated in FIG. 3 B. This figure shows prominences on each tooth surface which, by focusing the magnetic flux, generate centering forces passively (without control or power) to provide radial bearing function with no contact.

This conceptually defines a bilateral linear/rotary converter which will find many applications seeking performance improvements, as friction and backlash are greatly reduced and environmental limitations are removed. The source of bias flux may be configured in many ways to assure magnetic flux passing between the two sets of teeth. Radially magnetized cylinders are available as molded shapes of high energy rare earth magnets.

The circular (helical) form not only results in a compact device but also allows the slightly off axis direction of the inclined surfaces and forces to be cancelled out to a true axial force. It also allows the control coil conductors to start and finish at nearly the same point minimizing conductor length. These parts, with mating surfaces, may be formed by many methods and/or machined by ordinary thread making equipment capable of forming internal and external threads. The surfaces may be covered or coated with non-magnetic material to prevent metal to metal contact and allow power off operability.

FIG. 4. shows the cross section of a mechanism including a device of the type described in this disclosure. This illustrates a “best mode” although the selection of most configurations is heavily application dependent, but many involve integration with a motor/generator as shown.

In this case the helical device is connected to the rotor of a permanent magnet motor/generator, the rotation of which causes the axial translation of the outer part of the helix. The outer cylinder has internally threaded teeth engaged to similarly pitch teeth on the outer surface of the central shaft. Two ring shaped permanent magnets at the ends of the helix causes magnetic flux to flow axially in both directions to neighboring teeth on the central shaft. This is the bias flux; with no control currents, the teeth pull forcibly together, one way or the other, the central position being highly unstable. A control coil, wound along the helix, is supplied with a current creating a magnetic flux adding to the bias flux on one side and subtracting from the bias flux on the other. This generates an axial force proportional to the difference in the square of the flux densities on each side and reverses direction as the current is reversed. By classical servo techniques, the inner and outer teeth can be controlled to stay equally separated and non-contacting. This allows relative motion along the helical path with little or no measurable friction and a high ratio conversion of torque and force Since the motions are virtually devoid of friction, no lubrication is required, no wear products are formed, long lifetime may be expected, and the control can reduce backlash to any desired level.

This provides a mechanical action where the torque of a motor is due to forces at the airgap radius which move a distance equal to its circumference while the axial motion is one tooth pitch. Since the force-distance product remains constant, the “mechanical advantage” can be calculated and found to be very large. Conversely, axial forces applied to the outer element can cause rotation of the shaft and a generator output. Magnetic bearings have been designed to have significant gaps, in this use of that technology in the manner just described the techniques can be applied to systems having essentially no mechanical clearance (with a magnetic gap), most of the attributes can be obtained by controlling the contact force to approach zero. The magnetic surfaces can be covered with non-magnetic material allowing the mechanical gap to be smaller than the magnetic gap.

LIST of DRAWINGS

FIG. 1. Single Axis (Axial) Magnetic Bearing

1.A Cross Section, showing constant bias flux supply from two permanent magnets and control coil in slotted outer high permeability element.

1.B Top View, without cover, showing circularly symmetric engaged high permeability parts with cutaway to show control coil and common facing surfaces.

FIG. 2. Cross Section of Magnetic Bearing Extended Axially

To increase working surface area and control active length by helical form.

FIG. 3. A&B Limited Cross Sections of Helical Form Magnetic Bearing as Part of Electromechanical Transformer.

Showing detail of central and outer tooth structure to illustrate the magnetic circuit geometry with permanent magnets supplying constant bias flux which divides and flows upwards and downwards between mating tooth surfaces. Current in the control coil surrounding central teeth induces flux flowing upwards or downwards through both upper and lower gaps depending only on the direction of current flow in the coil. The axial forces generated by the difference in flux densities on opposite surfaces of the central teeth produce the controllable forces in accordance with the position sensor information to maintain centered, non-contacting position between the teeth.

FIG. 3.B This illustrates the same view with the addition of raised promontories on all mating tooth surfaces. These circular mating surfaces can increase the magnetic radial centering forces for passive control.

FIG. 4. Cross Section of an Electromechanical Transformer

With permanent magnet biased helical form magnetic bearing, with control coil leads, integrally connected to a conventional motor/generator, standard radial bearings, and an electro magnetic axial position sensor.

NUMBERING of PARTS

-   -   1. A SOURCE of CONSTANT MAGNETIC FLUX     -   2. A TYPICAL LINE OF MAGNETIC FLUX     -   3. A TYPICAL LINE OF CONTROL FLUX     -   4. A CROSS SECTION OF CURRENT CARRYING CONDUCTORS     -   5. CROSS SECTION OF CENTRAL HIGH PERMEABILITY ELEMENT     -   6. CROSS SECTION OF OUTER HIGH PERMEABILITY ELEMENT     -   7. UNIFORM CIRCUMFERENTIAL AIRGAP     -   8. LOWER AXIAL AIRGAP     -   9. UPPER AXIAL AIRGAP     -   10. DEPTH OF ENGAGEMENT     -   11. PROMONTORIES ON TEETH     -   12. SENSOR MEASURED POSITION 

1. I claim to have originated a new and useful device consisting of two wedge-like mating surfaces electronically controlled to maintain their separation constant by means of electromagnetic forces, allowing free motion along this diagonal path.
 2. I claim to be unique and original to me, a spiral form of thread-like mating surfaces with controlled electromagnetic forces holding the separation distance constant while allowing free motion along this prescribed path.
 3. I claim as unique and original to me, a device which, by means of electromagnetic forces, maintains the working surfaces of tooth-like elements to be equally spaced, reducing or eliminating backlash or position error in reversing or oscillating systems.
 4. I also claim the device of claim 2 which is made part of an actuator to produce controllable axial forces or motion by rotary means.
 5. I also claim the device of claim 2 which is part of a device to convert axial force or motion to rotational motion.
 6. I also claim the device of claim 2 to be used for displacement or force multiplication.
 7. I also claim the device of claim 2 to be used for axial to rotary motion conversion, or force to torque.
 8. I also claim the device of claim 2 to be used for rotational to axial motion or force conversion.
 9. I also claim the device of claim 2 to be used to enhance the effective area and force capability of a given diameter magnetic bearing or electromechanical transformer.
 10. I also claim the device of claim 2 in which the magnetic field bias flux is provided by electromagnet means either in conjunction with the control coils or independently.
 11. I also claim the device of claim 2 with the control force is produced by controlled currents interacting with magnetic flux independently or in conjunction with forces related to the square of the flux density.
 12. I also claim the device of claim 2 in which there is no separation between the controlled sliding parts other than lubricating films or low friction plastic
 13. I claim a device using magnetic bearing technology to reduce the friction of wedges as simple machines.
 14. I also claim the device of claim 13 as applied to helical shaped surfaces.
 15. I also claim the device of claim 13 when the magnetic bearing technique employs permanent magnets to supplement control flux provided by currents to effect suspension.
 16. I also claim the device of claim 14 when said helical surfaces are concentric surfaces as typical matching screw and bolts.
 17. I claim a device consisting of concentric helices capable of bidirectional rotary/linear motion conversion without physical contact.
 18. I also claim the device of claim 17 in which the helices are kept from metallic contact by means of magnetic forces.
 19. I also claim the device of claim 17 in which the mating surfaces are kept concentric passively by constant magnetic flux sources.
 20. I also claim the device of claim 17 in which axial forces are produced by the interaction of constant magnetic flux and magnetic fluxes controlled with respect to a displacement sensor.
 21. I claim a device of concentric helices with magnetically controlled separation having little or no friction.
 22. I also claim a rotary/linear motion converter of claim 21 in which the coefficient of friction is electrically switchable.
 23. I claim a linear/rotary converter to efficiently convert axial motions to the rotation of an ordinary generator or alternator capable of useful work.
 24. I also claim the device of claim 23 to produce a velocity dependent output, proper for absorbing shocks.
 25. I also claim the device of claim 23 to handle reciprocating motions with long-lived wear free operation.
 26. I claim a device using a system of electromagnetics to vary the contact force between surfaces in relative motion to adjust the coefficient of friction.
 27. I also claim the device of claim 26 to modify the operating characteristics of bidirectional linear/rotary converters.
 28. I also claim the device of claim 26 which can be electrically switched from efficient power transmission to a friction locked condition. 